Preparation, Modification And Properties Of Zno Nanowire Arrays

As a traditional semiconductor, ZnO have attracted intense interests due to its uniquecatalytic, electricity, photo-electricity performances. Recently, ZnO nanwire arrays haveshown great potentials as building blocks of nanodevices due to the excellent properties,such as single crystalline, efficient charge transport, high transparency, etc. In thisdissertation, highly aligned ZnO nanowire arrays were firstly synthesized throughhydrothermal method reported by other groups. Then, by modifying the as-prepared ZnOnanowire arrays, a better performance in application of photoelectrochemical nano-deviceswas seeked.The main parts of the thesis are as follows:1. Highly aligned ZnO nanowire arrays were firstly fabricated via hydrothermalmethod. The SEM images indicate that as-synthesized ZnO nanowires have lengths of1-2μm and diameters range from100-200nm. The density, diameter and length of ZnOnanowires can be readily controlled by changing reaction parameters. The formationmechanism of ZnO nanowire arrays was also proposed.2. We demonstrate that uniform Ag nanoparticles could be directionally grafted on thetip of ZnO nanowire arrays by a simple photo-reduction method. Furthermore, the structure,position, and amount of Ag nanoparticles grafted on ZnO nanowire array could be furtherrationally tailored by changing the reaction parameters such as the category, concentrationof reagents, and annealing temperature. Moreover, their photoelectrochemical performancesunder both UV-vis and monochromatic light irradiation have been explored. Interestingly,the photocurrent density of Ag/ZnO heterostructures could achieve up to2.40mA cm-2,which is much higher than that of pure ZnO nanowire array. It has been proposed that theformation of ZnO nanowire array tip-grafted with Ag nanoparticles could promote theeffective separation and directional transfer of photoexcited electron–hole pairs, and thusenhance the photoconversion properties.3. We have demonstrated for the first time that ZnO nanowire arrays could berationally connected with each other by thin Au nanowires to construct a novel cross-linkedhetero-structure via a simple photo-reduction strategy. Moreover, a possible formationmechanism of this Au/ZnO hierarchical nanostructure has been proposed. In the case oflight irradiation, the rapid electron enrichment on the top (002) facets of ZnO nanowires will result in the high concentration holes on side facets, which could generate a positive electricfield. As a result of the electronegativity,[Au(OH)xCl4x]-(where x=0-4) anions could bepulled in this electric field and reduced on side facets of ZnO nanowires, and the Aunanowires could be gradually formed via exact opposite point growth route. Furthermore,the photoelectrochemical performance studies clearly reveal that these novel cross-linkednanocomposites exhibit much higher visible light photocurrent density than both pure ZnOnanowire arrays and traditional Au nanoparticles/ZnO nanowire heterostructures, whichmay be primarily ascribed to the efficient electron transfer from Au nanostructures into ZnOnanowires.